The mechanisms whereby anaerobes such as Bacteroides survive brief transit through an oxidizing environment to establish a soft tissue infection or external trauma have not been investigated. Any anaerobe possessing even meager defenses against oxygen would more likely remain viable in an oxygen environment and could be more frequently involved in soft tissue infections. The effects of catalase and superoxide dismutase in oxygen tolerance of selected anaerobes will be studied. Catalase levels may be manipulated nutritionally by varying the amount of hemin in the medium. There is a marked protection against hyperbaric oxygen toxicity and H2O2 lethality in cells whose catalase levels have been induced. Studies are currently underway to determine whether superoxide dismutase levels can be elevated by exposure of the cells to low O2 levels and whether both catalase and superoxide dismutase can be elevated simultaneously. The resistance to O2 stress will be determined in those test systems.